Retention skirt for pacing electrode assembly

ABSTRACT

The electrode assembly is mounted at the distal end of a pacing lead comprising a lead body and at least one wire conductor in the lead body. The assembly comprises a tip electrode including a tip and a connection to the wire conductor and a skirt extending around the lead body and backwardly from the tip. The skirt has at least two slits extending axially therein from the rearward edge thereof to separate the skirt into at least two adjacent separated skirt sections. The skirt also can have one or more annularly and radially extending spurs which are adapted to engage trabeculae in a heart chamber for anchoring and maintaining the electrode assembly in place. The skirt sections allow and enhance removal of the electrode assembly when desired by the application of sufficient tension to the pacing lead to cause the skirt sections to fold back over themselves as the pacing lead is withdrawn from the body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flexible retention skirt which formspart of an electrode assembly at the distal end of a pacing lead andwhich serves to hold an electrode tip of the assembly in a desiredposition within a heart.

2. Description of the Prior Art

Heretofore, various structures have been proposed for maintaining anelectrode tip of an electrode assembly at the distal end of a pacinglead in a desired position within a heart. For example, in U.S. Pat. No.3,902,501, there is disclosed an endocardial electrode having aplurality of pliant tines which are held against the electrode bodyduring insertion and which are released and allowed to spread out whenthe electrode tip is in a desired position within a heart.

Also, in U.S. Pat. No. 3,719,190, there is disclosed a heart stimulationelectrode with a conical positioning parachute which, when the electrodeis inserted in a vein, permits blood flow in the vein to draw theelectrode through the vein into the heart so that the electrode may beused with an external power source for stimulating the heart. Whensufficient tension is applied to the pacing lead, the parachute willeventually invert to permit withdrawal of the electrode but will notreturn to its original shape in a heart cavity once it is inverted.

As will be described in greater detail hereinafter, the flexibleretention skirt of the present invention provides for stable positioningof an electrode at the tip of an electrode assembly at the distal end ofa pacing lead in a heart chamber, e.g. the atrium, by having a formationwhich engages heart tissue to minimize sliding back of the electrode,while at the same time having separable sections or being in the form ofa partial skirt which facilitates removal of the electrode assembly whenit is desired to do so by pulling on the pacing lead causing each skirtsection or partial skirt to fold back over itself on retraction of thepacing lead and which sections or partial skirt will return to their orits' original orientation when the skirt is in an open space in a heartchamber for repositioning of the assembly in the heart chamber.

SUMMARY OF THE INVENTION

According to the invention, there is provided an electrode assembly,adapted to be mounted at the distal end of a pacing lead including atubing and an electrical wire conductor in the tubing, comprising atleast a tip electrode including a tip and means for connecting said tipto the wire conductor, a body coupled to the tubing and mounting saidtip electrode and a skirt extending around and outwardly of said body,extending rearwardly from said tip and having in the rearward portion ofsaid skirt, at least two slits for separating said skirt into at leasttwo separated sections, said skirt being capable of engaging trabeculaein a heart chamber for maintaining said electrode assembly in place, andsaid separated skirt sections facilitating folding over of said skirt toallow said electrode assembly to be removed when desired by applicationof sufficient tension to the pacing lead to cause said skirt sections tofold back over themselves as the pacing lead is withdrawn.

Further, according to the invention, there is provided an electrodeassembly, adapted to be mounted at the distal end of a pacing leadincluding a tubing and an electrical wire conductor in the tubing,comprising a tip electrode including a tip and means for connecting saidtip to the wire conductor, a body coupled to the tubing and mountingsaid tip electrode, and a skirt extending at least part way around andoutwardly of said body and extending rearwardly from said tip, saidskirt having at least one spur thereon extending radially outwardly fromthe outer surface of said skirt in an arc about the elongate axis ofsaid electrode assembly, said at least one spur on said skirt beingcapable of engaging trabeculae in a heart chamber for maintaining saidelectrode assembly in place.

Also according to the invention there is provided an electrode assemblyadapted to be mounted at the distal end of a pacing lead. The assemblycomprises at least a tip electrode and a skirt extending at least partway around the assembly and extending rearwardly from the tip electrode.The skirt has two or more openings through the skirt to form spacedapart easily foldable skirt portions between the openings, and iscapable of engaging trabeculae in a heart chamber for maintaining theelectrode assembly in place. The openings and the skirt portionstherebetween facilitate folding over of the skirt to allow the electrodeassembly to be removed when desired by the application of sufficienttension to the pacing lead to cause the skirt to fold back over itselfas the pacing lead is withdrawn.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a pacing lead with an electrode assemblyhaving a tip electrode and a retention skirt constructed according tothe teachings of the present invention situated at the distal end of thepacing lead.

FIG. 2 is an enlarged perspective view of the tip electrode and theretention skirt shown in FIG. 1 with a portion of the pacing leadextending from the skirt broken away.

FIG. 3 is a sectional view of the tip electrode and the retention skirtshown in FIG. 2.

FIG. 4 is a side elevational view of another embodiment of an electrodeassembly comprising a tip electrode and a retention skirt constructedaccording to the teachings of the present invention.

FIG. 5 is a perspective view of still another embodiment of an electrodeassembly comprising a tip electrode and a retention skirt constructedaccording to the teachings of the present invention.

FIG. 6 is a part sectional view of the retention skirt of the electrodeassembly shown in FIG. 5.

FIG. 7 is a side view of the tip electrode and retention skirt shown inFIG. 5.

FIG. 8 is a perspective view of a further embodiment of an electrodeassembly comprising a tip electrode and a retention skirt constructedaccording to the teachings of the present invention situated at thedistal end of a J-atrial pacing lead.

FIG. 9 is an enlarged perspective view of the tip electrode andretention skirt shown in FIG. 8 viewing same from the inside of the J.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in greater detail, there is illustrated inFIG. 1, a pacing lead 10 having an electrode assembly 12 which ismounted at the distal end thereof, and which is constructed according tothe teachings of the present invention.

As shown in FIGS. 2 and 3, the electrode assembly 12 includes a tipelectrode 14 and a retention cuff or skirt 16 which extends rearwardlyfrom near the backside 18 of the tip electrode 14 and flares outwardlyat an angle between 20° and 40° and preferably 30° to the elongate axisof the assembly 12, to form the skirt 16 with a generally conical shape.

The retention skirt 16 is constructed in accordance with the teachingsof the present invention and has a forward edge 20 which abuts thebackside 18 of the tip electrode 14. The skirt 16 extends conicallyrearwardly preferably a length of approximately 0.220×0.05 inch, fromthe tip electrode 14 about or within a terminal pin or shank 22 thatextends rearwardly from and is integral with the tip electrode 14. Theskirt 16 extends about a distal end portion 24 of a pacing lead body 26and axially rearwardly to a rearward edge 28 of the skirt 16.

According to the teachings of the present invention, the retention skirt16 has at least two, and in the illustrated embodiment, four slits 31-34extending from the rearward edge 28 axially of the retention skirt 16toward the forward edge 20 of the retention skirt 16 but not all the wayto the forward edge 20. Each slit 31-34 will terminate a short distancebefore the forward edge 20 at an end 40 as shown in FIG. 2 and extendsfor 80 to 90% of the length of the skirt 16.

The slits 31-34 divide the retention skirt 16 into four sections 41-44,each of which has a radially outwardly extending annular quarter sectionspur 50. By annular quarter section is meant the spur 50 extends in, andon each skirt section 41-44 about the elongate axis of the assembly 12through an arc of approximately 90°. As shown, each spur 50 is spacedinwardly from the rearward edge 28 of the skirt 16 and separated fromthe rearward edge 28 by a quarter section annular shoulder 52 in theskirt 16. Preferably, the spur 50 has a height L₁ of approximately 0.020inch from shoulder 52 which has a width L₂ of approximately 0.020 inch.

Referring now to FIG. 3, it will be apparent that the retention skirt 16also has a barrel or sleeve portion 54 which extends directly rearwardlyfrom the forward edge 20 of the retention skirt 16, preferably adistance L₃ of approximately 0.165 inch and about the distal end portion24 of the pacing lead 10. The barrel portion 54 serves to hold thedistal end portion 24 of the pacing lead 10 about and in contact withthe terminal pin or shank 22 extending rearwardly from the tip electrode14 as shown.

The pacing lead 10 is of conventional construction and includes a coilof one or more wires or conductors, or as they are known in the art,filars 56, and the filars 56 at the distal end portion 24 of the pacinglead 10 have the insulation removed therefrom and are in mechanical andelectrical contact with the shank 22. The inner diameter of the barrelportion 54 has the same diameter or a slightly smaller diameter than theouter diameter of the shank 22 so as to exert pressure on the shank 22and/or lead body 26.

Also, if desired, each of the sections 41-44 of the retention skirt 16can have an opening 58 therein to facilitate more the bending or foldingover of the skirt sections 41-44 on themselves. Preferably, and asshown, each opening 58 is generally oblong in shape with each oblongopening 58 extending in a direction generally axially of the electrodeassembly 12. Also, in one embodiment, each oblong opening 58 has alength of approximately 2/3 the length of the skirt 16. Such openings 58are optional, however.

In one realization of the skirt 16, the skirt 16 was made of medicalquality silicone rubber and had a length of approximately 0.220×0.05inch and a thickness of approximately 0.015 to 0.020 inch. The barrelportion 54 had a length of approximately 0.165 inch. The spur 50 had aheight L₁ of 0.015 inch and a width at its base of approximately 0.015inch. The width L₂ of the shoulder 52 was approximately 0.020 inch. Theback edge 28 was made normal to the axis of the electrode assembly 12but preferably could have had a conical chamfer 59 at an angle α ofapproximately 60° to the axis of the assembly 12 as shown.

Also, one additional spur 60 with the same approximate dimensions ofspur 50 was provided on each skirt section 41-44 as shown in phantom inFIG. 3. It may even be desirable to provide a third quarter annular spur62 on each skirt section in addition to spurs 50 and 60.

In the embodiment of the electrode assembly 12 having the retentionskirt 16 as shown in FIGS. 1-3, the electrode assembly 12 of the pacinglead 10 is inserted into the heart, such as through a vein, and when itis in proper position within a chamber of the heart, such as the atriumor ventricle, the physician makes tests to make certain that the tipelectrode 14 is making proper contact with the endocardium forstimulating heart muscle tissue.

When the electrode assembly 12 is in proper position, the rearward edge28 of the skirt 16, preferably with the chamfer 59, and back side 61 ofeach spur 50 adjacent shoulder 52 will engage trabeculae of the heartand serve to hold or maintain or retain the electrode assembly 12 in thenow determined desired position. The back side 61 of each additionalspur 60 will provide and serve the same function, namely, an anchoringfunction.

However, at a later time, it may be desirable to remove the electrodeassembly 12 and pacing lead 10 and the slits 31-34 forming the skirtinto four sections 41-44 facilitate and enable the pacing lead 10 to beeasily removed from the heart merely by applying tension to the outerend of the pacing lead 10 and pulling it out of the heart. When thisoccurs, each section 41-44 of the skirt 16 will, when it is urgedagainst the tissue, fold over on itself. The weakened area of each skirtsection 41-44 between the front end of adjacent slits 31-34 created bythe oblong opening 58 in each section 41-44 further facilitates thisbending over. Then, further pulling of the pacing lead 10 will allow thepacing lead 10 to be pulled out of the heart chamber with the skirtsections 41-44 folded over on themselves.

Additionally, the opening 58 may also function as a holding means whichprovide for fibrotic growth therein to better hold the electrodeassembly 12 with skirt 16 in place.

Also, it will be appreciated that for relocating the assembly 12 in aheart chamber once the assembly 12 has been dislodged from heart tissue,such as in the appendage of the atrium, by pulling on the lead body 26,the skirt sections 41-44 will resume their normal positions as shown inFIGS. 1-3 to permit relocating and reanchoring of the assembly 12.

Referring now to FIG. 4, there is illustrated therein, another electrodeassembly 70 constructed in accordance with the teachings of the presentinvention. This electrode assembly 70 has a tip electrode 72 similar oridentical to the tip electrode 14 shown in FIGS. 1-3 and a skirt 74which extends from a back side 76 of the tip electrode 72 conicallyrearwardly from the tip electrode 72 to a rearward edge 78 thereof. Thisretention skirt 74 is very similar to skirt 16 shown in FIG. 2 in thatit has four sections 91, two of which are shown. Here, instead of havinga slit, or at least two slits, the retention skirt 74 of FIG. 4 has atleast two, and preferably four, axially extending notches 100 thereinwhich extend from the rearward edge 78 of the skirt 74 inwardly toward,but not all the way to, the forward edge 110 of the retention skirt 74.Also, each notch 100 has a rear portion 112 which has one dimension anda forward portion 114 which tapers from the rear portion 112 to arounded forward end 116 of the notch 100. If desired, the side of eachnotch 100 can be parallel without forward portion 114 and terminate in aradius. Also, the retention skirt 74 has a barrel portion 118 which isreceived over the distal end portion 24 of the pacing lead 10 in asimilar manner as the barrel portion 54 shown in FIG. 2 and has fourspurs 119.

In this embodiment, with the retention skirt 74 having notches 100,instead of slits 31-34, no oblong openings are provided such as theoblong openings 58 shown in FIGS. 2 and 3. However, if desired, oblongopenings could be provided in the skirt sections 91. Alternatively,slits, like slits 31-34 of skirt 16 in FIG. 2, can be provided in theskirt 74 in addition to notches 100. The addition of slits may bepreferred over openings 58.

The dimensions of the skirt 74 can be approximately the same as forskirt 16 and one or two additional spurs 119 can be provided on eachskirt section 91 to assist in the anchoring of the assembly 70.

Referring now to FIGS. 5-7, there is illustrated therein, anotherembodiment of the electrode assembly of the present invention which isgenerally identified by the reference numeral 120. Here, the electrodeassembly 120 has a tip electrode 122 similar to or the same as the tipelectrodes 14 and 72 shown in FIGS. 3 and 4. However, in thisembodiment, a retention skirt 124 modified somewhat from the retentionskirt 16 shown in FIG. 3 is provided. Here, the retention skirt 124 hasa forward edge 126 and a rearward edge 128. However, this conicallyshaped retention skirt 124 differs by having one spur formation 132extending outwardly from the rear edge 128 of each skirt section 134 asshown. If desired, each skirt section 134 can have one or two additionalspurs with the spurs extending around the skirt 132 at the same axiallocation of the spurs, e.g. spur formations 132, forming an annularcollar about the skirt 124.

This retention skirt 124 is generally conical and is provided with eightslits 136 therein to divide the skirt 124 into the eight sections 134.Also, each section 134 can be provided with an oblong opening 150extending axially of the electrode assembly 120 and skirt 124 thereof,if desired.

As shown in FIG. 6, the skirt 124 is also provided with a barrel orsleeve portion 160 which extends directly rearwardly from the tipelectrode 122 and is configured and dimensioned so as to receivetherein, distal end portion 162 of a pacing lead 164.

In this electrode assembly 120 where eight skirt sections 134 areprovided, such sections 134 have a shorter width that may furtherfacilitate withdrawal of the electrode assembly 120 from a heartchamber. In this respect, if obstructing tissue is encountered, only oneor two of the skirt sections 134 may be forced to fold over while theothers will remain in the position shown while the electrode assembly120 is being retracted from an anchored position.

Also, although only one spur formation 132 is shown on each skirtsection 134, as noted above, one or two additional spurs can be providedon each skirt section 134 to assist in the anchoring thereof intrabeculae.

To further minimize trauma to tissue and yet at the same time provide aretention function, it may be desirable to provide an electrode assemblywith a retention skirt that does not extend completely around theelectrode assembly and distal end portion of a pacing lead. Such aconstruction of an electrode assembly is shown in FIGS. 8 and 9 and isgenerally identified by reference numeral 170. Here, a distal endportion 172 of a J-atrial pacing lead 174 is shown provided with aJ-shaped set as shown in FIG. 8. Then, at the distal end 175 of the lead174, there is mounted the electrode assembly 170 comprising at least atip electrode 176 and a retention skirt 178 which has a semi-conicalconfiguration as shown. Here again, the retention skirt 178 includes abarrel portion 180 which extends from a forward end 182 of the skirt 178rearwardly in line with the tip electrode 176 a short distance forreceiving the distal end 175 of the J-atrial pacing lead 174 for holdingsame within the electrode assembly 170 and about a terminal pin or shank(not shown) extending rearwardly from the tip electrode 176. Thesemi-conical retention skirt 178 then extends conically or in a flaredmanner rearwardly from a forward edge 182 of the skirt 178 to asemi-circular rearward edge 184 thereof and on the outside of theJ-shaped distal end portion 172 as shown in FIG. 8. A spur formation 183extends radially outwardly from the rearward edge 184 as shown.

It will be noted that this retention skirt 178 is very similar to theretention skirt 74 shown in FIGS. 5-7 except that half of the skirt isremoved. In this embodiment of the electrode assembly 170 and skirt 178,three slits 191 are provided so as to divide the skirt into foursections 201. Also, each one of the sections 201 is provided with anoblong opening 211 extending axially of the skirt and electrodeassembly.

Although shown with three slits 191, it may be desirable to provide onlyone slit 191 so as to divide the skirt into only two sections 201. Stillfurther, it may be that no slits are needed in this embodiment sinceonly a partial or half skirt 178 is provided, which, because of one ormore oblong openings 211 therein, can easily fold over on itself whenthe pacing lead 174 is withdrawn from the body and will easily return toits original position.

The partial skirt 178 or sections 201 thereof are preferably providedwith one or more additional partially annular spurs similar to spurformation 183. Further, the partial skirt 178 will extend around theaxis of the electrode assembly 170 through an arc of approximately 170°to 200° on the outside of the J. It could, if desired, extend on theother side or inside of the J. Also, skirt 178 can be provided with orwithout oblong openings 211 and with or without slits 191. Preferably,skirt 178 is provided with two slits 191, three sections 201 and threeoblong openings 211. Otherwise, the skirt 178 has dimensions similar tothe dimensions of skirt 16 shown in FIGS. 1-3 and is made of medicalquality silicone rubber.

In use, the distal end portion 172 of the lead 174 is straightened witha stylet and inserted in the atrium of a heart. Then the stylet iswithdrawn and the distal end portion 172 resumes its J shape set asshown in FIG. 8. The pulling back on the lead 174 will pull the tip ordistal end 175 into the appendage of the atrium. The skirt 178 on theoutside of the J forces the electrode to one side of the appendage andinto good electrical contact with heart tissue.

In positioning any of the electrode assemblies 12, 70, 120 and 170 shownrespectively in the various FIGS. 1-9, it is usually necessary to use astylet 220 (FIG. 2) which is inserted through cylindrical envelope orlumen 222 (FIG. 2) which exits within coiled filars 56 within the pacinglead body 26.

After the pacing lead is first inserted into a body with a stylet 220,the stylet 220 is then manipulated by a physician to place the electrodeassembly 12, 70, 120, or 170, and more particularly, the tip electrode14, 72, 122, 176 thereof, into a proper desired position so that it cancontact the myocardium in a heart chamber, such as the atrium.

A portion of the stylet 220 received within the pacing lead 10, 164, 174is shown in FIG. 2. Once a tip electrode is properly located in a heartchamber, the stylet 220 is removed from the various assemblies and theretention skirt e.g. skirts 16, 74, 124, 178 of the present invention asshown in the respective FIGS. 1-9 serve to hold the electrode assembly,e.g., assemblies 12, 70, 120, 170 anchored in place with the tipelectrode 14, 72, 122, 176 in good electrical contact with heart tissue.

From the foregoing description, it will be apparent that the electrodeassembly 12, 70, 120 or 170 of the present invention, and particularlythe novel retention skirt 16, 74 124 or 178 thereof, provide a number ofadvantages, some of which have been described above and others of whichare inherent in the invention. Most importantly, the skirt 16, 74 124 or178 provides means for facilitating and assisting anchoring andretention of the electrode assembly 12, 70, 120, 170 in place within achamber of the heart, particularly the atrium, while at the same timepermitting each retention skirt to be distorted and folded over onitself when it is desired to remove the electrode assembly 12, 70, 120,170 from the heart chamber by pulling the pacing lead 10, 164, 174,followed by return of the skirt 16, 74, 124 or 174 to its original shapewhen disposed in an open space within a heat chamber thereby permittingrepositioning and reanchoring thereof.

Moreover, it will be apparent that modifications can be made to theelectrode assembly 12, 70, 120 or 170 and novel flexure retention skirt16, 74, 124 or 178 thereof, without departing from the teachings of thepresent invention. Accordingly, the scope of the invention is only to belimited as necessitated by the accompanying claims.

I claim:
 1. An electrode assembly, mounted at the distal end of a pacing lead comprising lead body and at least one electrical wire conductor in the lead body, at least a tip electrode including a tip and means for connecting said tip to the wire conductor, and a skirt coupled to the lead body adjacent said tip and extending around and outwardly of said lead body, extending rearwardly from said tip and having in the rearward portion of said skirt, at least two slits for separating said skirt into at least two adjacent, but physically separated sections, said slits extending radially through said skirt and axially forwardly from a rear edge of said skirt toward but not to a forward edge of said skirt, said skirt being made of a flexible material and yet being capable of engaging trabeculae in a heart chamber for maintaining said electrode assembly in a desired position in a heart chamber, said adjacent, but physically separated skirt sections facilitating folding over of said skirt to allow said electrode assembly to be removed when desired by the application of sufficient tension to the pacing lead to cause said adjacent, but physically separated skirt sections to fold back over themselves independent from each other as the pacing lead is withdrawn and said adjacent, but physically separated skirt sections, when in an open space, being capable of returning to their original position independent of each other.
 2. The electrode assembly of claim 1 wherein said skirt has four slits therein.
 3. The electrode assembly of claim 1 wherein at least one of said sections has a hole therein which facilitates folding over of the said section onto itself on removal of said assembly.
 4. The electrode assembly of claim 3 wherein said hole is oblong in the axial direction of said skirt.
 5. The electrode assembly of claim 3 wherein each of said sections has a hole therein.
 6. The electrode assembly of claim 1 wherein at least one of said skirt sections has at least one generally radially outwardly extending spur.
 7. The electrode assembly of claim 6 wherein each skirt section has at least one spur extending radially outwardly therefrom.
 8. The electrode assembly of claim 7 wherein each skirt section has at least two axially spaced spurs thereon, each spur extending radially outwardly from said skirt and in an arc partially around the elongate axis of said electrode assembly.
 9. The electrode assembly of claim 7 wherein each skirt section has at least three axially spaced spurs thereon, each spur extending radially outwardly from said skirt section in an arc about the elongate axis of said electrode assembly.
 10. The electrode assembly of claim 1 wherein said skirt is formed of a material generally inert to body fluids such as a medical quality silicone rubber.
 11. The electrode assembly of claim 1 wherein said skirt has a thickness of between approximately 0.015 and approximately 0.020 inch.
 12. The electrode assembly of claim 7 wherein each said skirt section has an arcuate shoulder adjacent the rear edge thereof.
 13. The electrode assembly of claim 12 wherein each said skirt section has a rear edge which is normal to the axis of said electrode assembly.
 14. The electrode assembly of claim 12 wherein each said skirt section has a rear edge which has a chamfer.
 15. The electrode assembly of claim 14 wherein said chamfer is at an angle of approximately 60° inclined toward said tip electrode and toward the axis of said assembly.
 16. The electrode assembly of claim 7 wherein said spur has one side that extends radially outwardly to an outer edge and another side which extends from said outer edge forwardly and inwardly to said skirt so as to form said spur with a generally triangular cross section and said one side extends approximately 0.020 inch from said annular shoulder to said outer edge.
 17. An electrode assembly mounted at the distal end of a pacing lead comprising a lead body and at least one electrical wire conductor in the lead body, a tip electrode including a tip and means for connecting said tip to the wire conductor, and a skirt coupled to the lead body adjacent said tip and extending at least part way around and outwardly of said lead body and extending rearwardly from said tip, said skirt having at least one spur thereon extending radially outwardly from the outer surface of said skirt in an arc about the elongate axis of said electrode assembly, said at least one spur on said skirt being capable of engaging trabeculae in a heart chamber for maintaining said electrode assembly in place.
 18. The electrode assembly of claim 17, wherein said skirt has at least two axially spaced spurs thereon, each spur extending radially outwardly from said skirt and in an arc about the elongate axis of said electrode assembly.
 19. The electrode assembly of claim 18, wherein each skirt has at least three axially spaced spurs thereon, each spur extending radially outwardly from said skirt and in an arc about the elongate axis of said electrode assembly.
 20. The electrode assembly of claim 17 wherein said spur is at or adjacent the rear edge of said skirt.
 21. The electrode assembly of claim 17 wherein said spur extends in an arc about said skirt and outwardly a distance of approximately 0.020 inch from the outer surface of said skirt.
 22. The electrode assembly of claim 17 wherein said skirt is made of a medical quality silicone rubber and has a thickness of between approximately 0.015 inch and 0.020 inch.
 23. The electrode assembly of claim 17 wherein said skirt has means to allow said skirt easily to be folded over to allow said electrode assembly to be removed when desired by the application of sufficient tension to the pacing lead to cause said skirt to fold back over itself as the pacing lead is withdrawn and to facilitate return of said skirt to its initial position when said electrode is in an open space within a heart chamber.
 24. The electrode assembly of claim 23 wherein said facilitating means comprises at least two spaced apart slits extending through part of said skirt and axially of said skirt from a rear edge thereof to divide said skirt into at least two separated sections.
 25. The electrode assembly of claim 17 wherein said spur has a generally triangular cross section with a back side extending radially outwardly from said skirt and radially of said elongate axis of said electrode assembly, and a front side extending forwardly and inwardly from the outer edge of said back side to the skirt outer surface.
 26. The electrode assembly of claim 17 wherein said skirt extends radially outwardly of and rearwardly from said electrode tip so as to form said skirt with a generally conical shape. 